<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div class="box">盒子1</div>
    <div class="box">盒子2</div>
    <div id="nav">
        <ul>
            <li>首页</li>
            <li>产品</li>
        </ul>
    </div>
    <script>
        //1. document.getElementsByClassName 根据类名获得某些元素集合
        var boxs = document.getElementsByClassName('box')
        console.log(boxs);

        //2. document.querySelector 返回指定选择器的第一个元素对象
        var firstBox = document.querySelector('.box')
        console.log(firstBox);
        var nav = document.querySelector('#nav')
        console.log(nav);
        var li = document.querySelector('li')
        console.log(li);

        //3. document.querySelectorAll() 返回指定选择器的所有元素对象集合
        var allBox = document.querySelectorAll('.box')
        console.log(allBox);
        var lis = document.querySelectorAll('li')
        console.log(lis);

    </script>
</body>

</html>